In the existing mobile terminating calls, when a called mobile device is moving from one MSC (Mobile Switch Center) to another MSC, an MTRR (Mobile Terminating Roaming Retry) service may be applied to the mobile terminating calls; when the MSC for the user to send LAU (location update) is different from the MSC paging the UE, the MTRR will also be applied to a 4G CSFB (Circuit Switched Fallback) mobile call.
According to the 3GPP protocol, when the gateway mobile switching center (GMSC) receives an instruction for retrying the mobile terminating call, the GMSC should terminate the ongoing CAMEL dialogue service, such that the CAMEL service is re-invoked due to MTRR.
Refer to FIG. 1 and FIG. 2. FIG. 1 schematically shows a mobile communication system configured to provide a CAMEL service, wherein a part of information flow during the call process is also illustrated, and FIG. 2 schematically shows a call flow diagram of obtaining a CAMEL service during an MTRR process.
Herein, the mobile communication system comprises at least one HLR (Home location Register), at least one gsmSCF (GSM Service Control Function), at least one gsmSRF (GSM Special Resource Function), one or more VMSCs (Visited Mobile Switch Center), and at least one GMSC (Gateway Mobile Switch Center).
Specifically, when a calling party pages a called party, with reference to FIG. 2, in the flow P1, the GMSC sends, to an HLR, SRI (Send Routing Information) containing called party device identification information and a roaming retry identification, so as to request the HLR for an suppress TCSI (Terminating CAMEL Subscription information) indicator of the CAMEL service available in the current network.
Next, in a flow P2 for establishing a CAMEL session, in sub-flow a, the HLR feeds back to the GMSC the suppress TSCI indicator containing the currently available CAMEL service.
Next, in the sub-flow b, the GMSC sends an initial detection point to the gsmSCF (also called SCP, Service Control Point).
Next, in the sub-flow c, the gsmSCF sends, to the GMSC, a Request Report BCSM (Basic Call Status Model) Event, so as to configure the event information including, but not limited to the following, for the GMSC: EDP-13R (T-Busy), EDP-14R (T_NoAnswer), EDP15-R (T_Answer) and EDP-18R (T_Abandon).
Next, in sub-flow d, gsmSCF sends Establish Temporary Connection information to the GMSC, wherein a particular number of qualifier fields of the information contain an SSPIP (Service Switching Point IP) IP routing address, for indicating the RBT ring.
Next, in sub-flow e, the GMSC sends an IAM (Initial Address Message) to the gsmSRF (also called assisting MSC) based on the Assisting SSPIP Routing Address.
Next, in sub-flow f, the gsmSRF feeds back, to the GMSC, an ACM (Address Complete Message)/ANM (Answer Message) based on an ISDN (Integrated Services Digital Network) User Part protocol. Wherein a voice channel from the gsmSRF to the calling party is established through a GMSC (see the single solid-line arrow portion in FIG. 1). With a RBT service as an example, music or ringtone is played to the calling party now.
Next, in sub-flow g, gsmSCF sends “Continue” to GMSC, so as to maintain the CAMEL dialogue.
Next, in sub-flow h, the GMSC sends, to the HLR, an SRI containing the suppress TCSI indicator, so as to ask the HLR for a MSRN (Mobile Station Roaming Number) of the called party device at the original VMSC.
Next, in the flow P3, the HLR sends PRN (Provide Roaming Number) information to the original VSMC, and receives a PRN acknowledgement information that is fed back from the original VMSC and that includes the MSRN of the called party device in the original VMSC. Wherein the PRN contains an IE (Information Element) supported by the MT roaming retry, wherein in respective flows shown in FIG. 2, it is required to determine whether a corresponding message contains the IE supported by a corresponding MT roaming retry, so as to determine whether a corresponding operation may be performed using the MTRR technology, which will not be detailed here.
Next, in the flow P4, the HLR feeds back the SRI acknowledgement information to the GMSC, that SRI acknowledgement information contains the MSRN of the called party at the original VMSC.
Next, in the flow P5, the GMSC sends an IAM containing the MSRN to the original VMSC based on the received MSRN.
Next, in the flow P7, after the original VMSC receives the IAM, paging the called party starts.
Preferably, in the flow P6, the location of the called device changes, and location update information is sent to a new VMSC to which the called device is migrated. Or, the location update information is sent to the new VMSC in conjunction with the Circuit Switch Fallback technology, wherein the flow P6 may be performed before or after P7.
Next, in flow P8, the new VMSC sends the update location information to the HLR.
Next, in flow P9, the HLR sends Cancel Location information to the original VMSC and receives confirmation information from the original VMSC.
Next, in flow P10, the HLR inserts a plurality of subscriber data into the new VMSC.
Next, in flow P11, after the original VMSC stop paging, it sends Resume Call Processing (Roaming Retry) information to the GMSC and receives a Resume Call Processing acknowledgement from the GMSC.
Next, in flow P12, the GMSC sends a release message to the original VMSC and receives a Release Complete message fed back from the original VMSC, so as to complete a release process of call connection.
Next, in flow P13, when the GMSC receives the Release Complete message from the original VMSC, it terminates the CAMEL session with the gsmSCF, and terminates a forward connection with the gsmSRF.
Next, in the flow P14, an operation similar to the above flow P1 is performed to send an SRI to the HLR to request for the suppress TCSI indicator of the CAMEL service available in the current network.
Next, in the flow P15, sub-flows a to h similar to which in the above flow P2 are re-performed, wherein the SRI sent to the HLR in the sub-flow h here contains the suppress TCSI indicator, but does not contain a roaming retry identification.
Then, in the flow P16, the HLR continues to insert a plurality of subscriber data into the new VMSC.
Then, in the flow P17, the HLR sends Update Location Acknowledgement Information to the new VMSC.
Then, in the flow P18, the HLR sends a PRN to the new VMSC.
Then, in the flow P19, the HLR receives a PRN acknowledgement information that is fed back from the original VMSC and contains the MSRN′ of the called party in the new VMSC.
Then, in the flow P20, the HLR sends an SRI Acknowledgement information containing the MSRN′ to the GMSC.
Then, in the flow P21, the GMSC sends an IAM containing the MSRN′ to the new VMSC based on the received MSRN′.
Next, in the flow P22, the new VMSC sets a call through interaction with the called device, and starts re-paging the called device after receiving the IAM.
However, this service process has many drawbacks, mainly has following several aspects:
1) prolonging the call setting time. Since this process not only needs retrying the MT mobile terminating call, but also needs recalling the CAMEL service; therefore, the setup time of the call will be prolonged; 2) wasting resources. As it has to first interrupt the CAMEL services before re-calling the CAMEL service so as to retry the mobile terminating call, which causes the communication load of the ss7 (Signaling System No. 7) of the MAP and CAP-based network; 3) degrading user experience. When the user is using a CAMEL service, e.g., using a RBT service, during the process of re-calling after the CAMEL service is terminated, the user will hear the ringtones twice, and the ringtones might be different, which may disturb the calling party. Such circumstance may likewise exist in the LTE network and occur when the 4G subscriber circuit domain falls back to 3G.